Add function to trim leading/trailing empty lines.

internal/frontmatter/frontmatter.go

@@ -3,10 +3,14 @@ package frontmatter
 import (
 	"fmt"
 	"strings"
+	"unicode"
+	"unicode/utf8"
 
 	"gopkg.in/yaml.v1"
 )
 
+var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
+
 // Frontmatter encapsulates cheatsheet frontmatter data
 type Frontmatter struct {
 	Tags   []string
@@ -24,7 +28,7 @@ func Parse(markdown string) (string, Frontmatter, error) {
 
 	// if the markdown does not contain frontmatter, pass it through unmodified
 	if !strings.HasPrefix(markdown, delim) {
-		return strings.TrimSpace(markdown), fm, nil
+		return TrimEmptyLines(markdown), fm, nil
 	}
 
 	// otherwise, split the frontmatter and cheatsheet text
@@ -42,3 +46,52 @@ func Parse(markdown string) (string, Frontmatter, error) {
 
 	return strings.TrimSpace(parts[2]), fm, nil
 }
+
+// TrimEmptyLines returns a slice of the string s, with all leading
+// and trailing lines removed, which consist only of white space as
+// defined by Unicode.
+func TrimEmptyLines(s string) string {
+	start := 0
+	newlinePos := -1
+	for ; start < len(s); start++ {
+		c := s[start]
+		if c >= utf8.RuneSelf {
+			return strings.TrimFunc(s[start:], unicode.IsSpace)
+		}
+		if c == '\n' {
+			newlinePos = start
+			continue
+		}
+		if asciiSpace[c] == 0 {
+			if newlinePos >= 0 {
+				start = newlinePos + 1
+			} else {
+				start = 0
+			}
+			break
+		}
+	}
+
+	stop := len(s)
+	newlinePos = -1
+	for ; stop > start; stop-- {
+		c := s[stop-1]
+		if c >= utf8.RuneSelf {
+			return strings.TrimFunc(s[start:stop], unicode.IsSpace)
+		}
+		if c == '\n' {
+			newlinePos = stop
+			continue
+		}
+		if asciiSpace[c] == 0 {
+			if newlinePos >= 0 {
+				stop = newlinePos
+			} else {
+				stop = len(s)
+			}
+			break
+		}
+	}
+
+	return s[start:stop]
+}

internal/frontmatter/frontmatter_test.go

@@ -93,3 +93,56 @@ To foo the bar: baz`
 		t.Errorf("failed to parse text: want: %s, got: %s", markdown, text)
 	}
 }
+
+// TestTrimEmptyLines assert that leading and trailing empty lines are removed
+func TestTrimEmptyLines(t *testing.T) {
+
+	// define for readability of the tests
+	blank := "\x20"
+	linefeed := "\x0A"
+
+	testCases := []struct {
+		input string
+		want  string
+	}{
+		// nothing to be trimmed
+		{"", ""},
+		{"a", "a"},
+		{" non empty line ", " non empty line "},
+		{" non empty line " + linefeed, " non empty line " + linefeed},
+		{" non empty line " + linefeed + " another non empty line ", " non empty line " + linefeed + " another non empty line "},
+		{" non empty line " + linefeed + " another non empty line " + linefeed, " non empty line " + linefeed + " another non empty line " + linefeed},
+		// trim leading empty lines
+		{linefeed + " non empty line ", " non empty line "},
+		{blank + linefeed + " non empty line ", " non empty line "},
+		{blank + linefeed + linefeed + " non empty line ", " non empty line "},
+		{linefeed + blank + linefeed + " non empty line ", " non empty line "},
+		{blank + linefeed + blank + linefeed + " non empty line ", " non empty line "},
+		{linefeed + " non empty line " + linefeed + " another non empty line ", " non empty line " + linefeed + " another non empty line "},
+		{blank, ""},
+		{linefeed, ""},
+		{blank + linefeed, ""},
+		{linefeed + blank, ""},
+		{blank + linefeed + blank, ""},
+		{linefeed + blank + linefeed, ""},
+		// trim trailing empty lines
+		{" non empty line " + linefeed + blank, " non empty line " + linefeed},
+		{" non empty line " + linefeed + blank + linefeed, " non empty line " + linefeed},
+		{" non empty line " + linefeed + blank + linefeed + blank, " non empty line " + linefeed},
+	}
+
+	for _, testCase := range testCases {
+		// parse the input
+		text, _, err := Parse(testCase.input)
+
+		// assert expectations
+		if err != nil {
+			t.Errorf("failed to parse input: %v", err)
+		}
+
+		// assert that the wanted output was returned
+		if text != testCase.want {
+			t.Errorf("failed to parse text: want: [%s], got: [%s]", testCase.want, text)
+		}
+	}
+}